The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

2300-year-old Roman road connecting the empire.

The yawning maw of this pagan visage is said to bite off the hands of liars.

This quirky UFO-shaped curiosity is often mistaken for the airport’s control tower.

This opulent hotel has been visited by Spider-Man, Charlie's Angels, and the Ghostbusters.

The bank that helped fund the Mexican-American War and the purchase of Alaska met its downfall after helping Augusto Pinochet launder money.

One critic described it as "middle Mussolini, early Ramses, and late Neiman-Marcus." Another called it an architectural "natural disaster."

Look closely and you’ll notice that the color changes a third of the way up the tower.

The little-known, 300-year history of the area includes former lives as a bustling tobacco port, parking lot, and industrial dump.

This robust fence in front of a historic Georgetown home is likely made from hundreds of recycled Revolutionary War firearms.

This stately mansion, built in 1787 by America's first Secretary of the Navy, is rumored to be one of the most haunted buildings in Washington, DC.

Legend has it that President Grant’s frequent drinking in the lobby gave rise to the term “lobbyist.”

Perhaps the most scandalous statue of America's first president.

The oldest building in the District of Columbia was preserved because of a mistaken connection to George Washington.

D.C.'s first central library was born out of a chance encounter with the philanthropist whose name it bears.

A museum cafe showcases Native American dishes and indigenous ingredients from across the Western Hemisphere.

The house where John Wilkes Booth conspired with his co-conspirators.

Largest Roman Catholic church in North America.

The Byzantine, pre-Columbian, and medieval art at this stately mansion are some of the most under-appreciated collections in D.C.

A wondrous old library overlooking the nation's capital.

The site of the climactic scene from the classic horror film is now a historic landmark.

Home to items never before seen by the public.

The approximate spot where the last Grand Master of the Knights Templar was put to death.

This 18th-century sundial was designed to calculate the date of Easter each year.